The first opinion poll since Britain's rulers warned Scots they would lose the pound if they voted to leave the United Kingdom showed a slight increase in support for independence ahead of a referendum on the issue scheduled for September 18.

Politicians in London have tried to undermine the case for independence by cautioning that breaking the 307-year-old union with England would make Scots poorer.

Scottish nationalists said that such tactics had provoked a backlash among Scots, though opinion polls continue to show that Scots would vote to stay in the United Kingdom.

A Survation/Scottish Daily Mail poll carried out on February 17 and 18 of 1,005 people found 37.7 percent support independence, which it said could be compared to 36.9 percent recorded in a PanelBase/Sunday Times poll carried out on January 29-February 6.

The Survation poll showed 46.6 percent would vote 'no' to independence, a decline from 48.5 percent in the PanelBase/Sunday Times poll.

The gap between those who would vote against and for independence narrowed to 8.9 percentage points from 11.6 percentage points in the earlier poll.

Survation said its results were best compared to the PanelBase/Sunday Times poll of 1,012 people rather than its own earlier surveys because it had changed its methodology to bring it into line with other major pollsters.

With seven months to go until voting day, pollsters say it would only take a small section of the 4 million electorate to change their minds for the result to change.SCOTLAND'S PLAN B?

Scottish nationalists, led by First Minister Alex Salmond, have promised Scots that independence will allow them to forge their own prosperity: keeping the pound, the queen and using North Sea oil revenues to bankroll the new Scottish state.

But in a closely choreographed campaign, Prime Minister David Cameron and finance minister George Osborne have warned that breaking the union would endanger stability and propel Scotland towards a poorer future without the pound.

Osborne, whose warning on the pound was supported by Britain's two other main political parties, has said that without the chance of keeping the pound, Salmond is now "a man without a plan."

The Survation poll showed that both "yes" and "no" voters had a strong preference for keeping the pound and that 65 percent of respondents wanted Salmond to come up with a Plan B for the currency.

"The Scottish people seem to be demanding to see what the Plan B would be," said Patrick Brione, director of research at Survation. "'No' voters are very uncertain about the future of the currency and that seems to be one of the main motivations in discouraging them from voting for independence."